If you’ve been around diesel trucks for more than five minutes, you’ve probably heard someone talk about compound turbos.
Maybe you’ve seen a Cummins spool instantly with a massive charger under the hood… or a Duramax making 900+ hp with ease. Compound setups are legendary in the diesel performance world — and for good reason.
But what exactly ARE compound turbos? How do they work? And are they really worth it for your Cummins, Powerstroke, or Duramax?
Let’s break it all down — in simple, easy-to-understand diesel-owner language.
What Are Compound Turbos?
A compound turbo system uses *two turbos* that work together to provide:
- Faster spool-up (better low-end power)
- More airflow (better top-end power)
- Lower EGTs under heavy load
- Smoother power delivery across the entire RPM range
One turbo handles low-speed response, while the other supports high horsepower. Instead of choosing between “a small turbo that spools fast” or “a big turbo that makes big power,” compounds give you BOTH.
This is why diesel owners love them — especially people who tow, daily drive, drag race, sled pull, or just enjoy making big power reliably.
Compound Turbos vs. Twin Turbos: They’re NOT the Same
This is one of the biggest points of confusion in the diesel world.
Compound turbos ≠ twin turbos.
- Twin turbos usually mean two turbos of the same size running in parallel. Each turbo feeds a separate bank (common on V6/V8 gas engines).
- Compound turbos run in SERIES — the first turbo feeds the second turbo.
Compounds multiply pressure, rather than splitting airflow. That’s why diesel engines, with their high boost tolerance, benefit SO much from compound systems.
How Compound Turbos Work (Easy Explanation)
Think of compound turbos like a team effort:
Turbo #1 — The “Small” Turbo (High Pressure Turbo)
- Spools fast
- Helps with low-end torque
- Great for towing and daily driving
Turbo #2 — The “Big” Turbo (Atmospheric Turbo)
- Moves huge amounts of air
- Supports high horsepower levels
- Keeps EGTs low under heavy load or high boost
Air flows through BOTH turbos, one after the other. The small turbo pressurizes it, then the big turbo pressurizes it AGAIN.
This creates a super-efficient, super-powerful, super-responsive setup ideal for diesel applications.
Why Diesel Engines Benefit from Compound Turbos
Compounds work great with diesels because diesel engines:
- Operate at high compression
- Can tolerate high boost safely
- Make big torque at low RPM
- Love lots of clean, cool air
That’s why Cummins, Powerstroke, and Duramax platforms respond so well to compound setups.
Compound Turbos for Cummins
Cummins 5.9 and 6.7 engines are legendary for compound builds because of their inline-six design and massive airflow demand. Common setups include:
- S300/S400 Compound Kits
- S400/S400 Compound Kits
- Add-a-turbo kits that integrate the stock turbocharger
Benefits on Cummins:
- Huge towing gains
- Instant spool with massive top-end power
- Lower EGTs when hauling heavy loads
- Excellent daily drivability
Compound Turbos for Powerstroke
For 6.4 Powerstroke owners, compounds are factory equipment — a major reason the 6.4 is such a fun engine to tune.
For 6.0 and 6.7 owners, aftermarket compound kits offer:
- More airflow for towing
- Cooler EGTs under heavy load
- Higher horsepower capabilities
The 6.7 Powerstroke especially benefits from compounds due to its strong bottom end and great fueling potential.
Compound Turbos for Duramax
Duramax engines (LB7 through L5P) LOVE compound turbo setups because of their VGT turbo design and high-flow cylinder heads.
Benefits include:
- Retaining the quick spool of the factory turbo
- Adding a large atmospheric turbo for airflow
- Much lower EGTs while towing
- Ability to hit 700–1,000+ horsepower with proper supporting mods
On Duramax trucks, compounds offer some of the best power-per-dollar gains in the diesel world.
Should You Install Compound Turbos?
Compounds are ideal for diesel owners who:
- Tow heavy and want cooler EGTs
- Want more low end, mid-range, and peak horsepower
- Plan to build a 600–1,000+ hp truck
- Want drastically improved airflow without increased turbo lag
If that sounds like you — compounds might be the best upgrade you ever make.
FASS Motorsports: Your Compound Turbo Experts
Whether you’re shopping compound kits, upgrading your fuel system, or building a full high-horsepower diesel, FASS Motorsports has the parts, expertise, and installation team to help bring your build to life.
We support Cummins, Duramax, and Powerstroke owners throughout Washington, Missouri, Franklin County, and the greater St. Louis area.
👉 Shop Performance Upgrades
👉 Stop by our showroom (address below)
Have Questions? We're here to help.
- Phone: (636) 429-7020
-
Email: info@fassmotorsports.com
FASS Motorsports
25 Town and Country Drive
Washington, MO 63090
